DESCRIPTION: The research I am conducting focuses on fundamental questions in hearing, and the neural mechanisms employed by the brain in the processing of communication sounds. In the natural world, the auditory system extracts critical signals, such as speech, from complex acoustic environments. This is accomplished through both mechanical and neurobiological filtering and processing. Some of this is accomplished within the ear and auditory nerve. However, a great deal is also accomplished through complex processing by the brain, and relatively little is known about this. A robust understanding of auditory processing in the brain is of clear significance to a wide range of health issues, including the development of effective therapeutic measures for the hearing impaired. I will use neurophysiological and anatomical methods to address questions about the processing of communication sounds in the brain. I will focus on the mechanisms by which temporal patterns in sounds are analyzed. Temporal patterns allow humans to localize and identify sound sources, and to process speech. It is thus not surprising that recent research has shown that the preservation of time-cues is critical in the engineering of effective cochlear implants. The applicant will use an animal model to carry out the research. The fish Pollimyrus (Mormyridae) is particularly appropriate because it uses simple temporally patterned sounds for communication, and has an auditory system that is dedicated to encoding time cues. This is a vertebrate species that can be relatively easily analyzed at both neurophysiological and anatomical levels. Recent experiments have shown that there are neurons in the brain whose activity depends upon specific temporal cues. Single cell neurophysiological recording techniques will be used to study these neurons, and to discover how their temporal selectivity originates. This will be done by recording in the brain (mesencephalon), while presenting a variety of acoustic stimuli, and while treating the neurons with neuroactive chemicals. Also to be examined are auditory responses in neurons that constitute an earlier stage of processing in the brain, to determine what the temporally selective cells receive as input.